Method for determining registration areas in a wireless communication system

ABSTRACT

A method for determining a plurality of location areas in a wireless communication system is disclosed. The method comprises the steps of determining a plurality of mobility data corresponding to a plurality of first partition units respectively and an overall cost of a plurality of first registration areas, wherein each of the first registration areas includes at least one of the first partition units; generating a plurality of second registration areas through a registration area determining procedure, wherein the second registration areas are constructed based on the mobility data of the first partition units; determining an overall cost of the second registration areas; comparing the overall cost of the first registration areas and the second registration areas; and determining a plurality of third registration areas and second partition units based on the result of comparison, wherein at least one of the second partition units is generated by combining at least two of the first partition units based on the mobility data of the corresponding first partition units when the overall cost of the first registration areas is lower than or equal to the overall cost of the second registration areas, at least one of the second partition units is generated by partitioning one of the first partition units based on the mobility data of the corresponding first partition units when the overall cost of the first registration areas is higher than the overall cost of the second registration areas.

BACKGROUND OF THE INVENTION

1. Technical Field

The proposed invention relates generally to a mobility management methodfor use in a wireless communication system; and more particularly to amethod for determining registration areas in a wireless communicationsystem.

2. Related Art

There has been a very rapid growth in the number of service areas andsubscribers in the wireless communications industry. The servicerequests (call attempts) received by mobile switching centers (MSC's)have been huge and kept growing especially in metropolitan areas.Therefore, mature and efficient Location (Mobility) Management plays asignificant role in the regular operation of a wireless communicationsystem.

Location (Mobility) Management is the procedure of keeping track of andlocating mobile stations (MS's) in a wireless communication system sothat calls arriving for them can be routed correctly to their currentlocation. The purpose of Location (Mobility) Management is then to trackthe MS's using minimum overhead traffic. Since the radio bandwidth is ascarce resource in mobile radio communication systems, it's thusimperative to develop efficient techniques for minimizing this overheadtraffic and thereby maximizing the revenue-generating traffic-carryingcapacity of the system.

The MSC, though keeping track of MS's currently operating in its servicearea via a visitor location register (VLR) database, doesn't usuallyhave accurate info as to the precise geographical location of each ofthe MS's within the service area. Consequently, when a call is initiatedto a MS within the service area, a page must be broadcast over all cellsin the service area. The paging message then has to be replicated acorresponding number of times and sent to each cell, but since there'sonly one cell in the system receiving a response from the MS, it meansthat a huge amount of radio bandwidth resources, thus additional costs,are over-wasted, which would otherwise be used for performing othertasks.

The conventional solutions to overcome this problem are to partition theservice area of the wireless communication system into a plurality ofregistration areas (RA's), which are smaller than the service area. Whena MS goes across the border of a RA and enters another RA, it willperform a location update (LU) indicating that it is operating withinthe newly entered RA. In this case, when a call is initiated to the MS,only the cells of that specific RA will be paged. But on the other hand,the number of LU's (with corresponding costs) will also be higher sincethe movements from one RA to another are more frequent. Therefore, atrade-off between paging and LU appears, and thus optimal RAformulation, i.e. the optimal determination of the boundaries (thelocation of borders between RA's) and the number of RA's are then verycrucial.

Although the concept is caught and technically put into practice by theconventional methods, however, most of them actually just came up with alocally optimal solution, which will be explained in detail in thefollowing paragraphs of the specification.

SUMMARY OF THE INVENTION

Therefore, there's an object of the present invention to provide aregistration area determining method in which the registration areas aredetermined to reach global near-optimality, i.e. the capacity of anyphysical or virtual equipments optimized (maximized) globally (forexample, paging load conformed to limited control channel resourcessystem-wise), and the traffic (from any traffic sources) between cells(or LA's, etc.) globally optimized such that the overall cost of thewireless communication system can be minimized.

According to the object of the present invention, a method fordetermining a plurality of location areas in a wireless communicationsystem is disclosed. The method comprises the steps of determining aplurality of mobility data corresponding to a plurality of firstpartition units respectively and an overall cost of a plurality of firstregistration areas, wherein each of the first registration areasincludes at least one of the first partition units; generating aplurality of second registration areas through a registration areadetermining procedure, wherein the second registration areas areconstructed based on the mobility data of the first partition units;determining an overall cost of the second registration areas; comparingthe overall cost of the first registration areas and the secondregistration areas; and determining a plurality of third registrationareas and second partition units based on the result of comparison,wherein at least one of the second partition units is generated bycombining at least two of the first partition units based on themobility data of the corresponding first partition units when theoverall cost of the first registration areas is lower than or equal tothe overall cost of the second registration areas, at least one of thesecond partition units is generated by partitioning one of the firstpartition units based on the mobility data of the corresponding firstpartition units when the overall cost of the first registration areas ishigher than the overall cost of the second registration areas. Otherobjects, features, and advantages of the invention will become apparentfrom the following detailed description of the preferred butnon-limiting embodiments. The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified diagram to represent a general mobility graphwhere each node represents any physical or virtual equipments with anytype of capacity info provided, and each edge represents any trafficsources (with statistics) between the nodes;

FIG. 2 is a diagram briefly showing one of the disadvantages of theconventional registration area partitioning methods;

FIG. 3 is a flow chart illustrating the operation of the registrationarea partitioning method according to the embodiment of the presentinvention.

FIG. 4˜FIG. 14 help illustrate the proposed method (procedure) step bystep in an example according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The Mobility Management problem is very often developed in terms of anode-capacitated graph-partitioning problem. Cells are modeled asweighted modes and the edges between them represent the cell-crossingrate of MS's, as shown in FIG. 1. The problem involves partitioningnodes of this graph, which is referred to as “mobility graph” here,under capacity restriction on the sum of the node weights in eachelement of the partition (i.e. a registration area). Each element of thepartition may be called as a “slot” of the partition.

In the present invention, a mobility graph such as FIG. 1 applies togeneral (node-capacitated) graph-partitioning scenarios where each node102 represents any physical or virtual equipments with any type ofcapacity info provided, and each edge 104 comprises a plurality ofmobility data at least including a plurality of mobility ratesdetermined by any “traffic” sources (with statistics) 106 between thenodes, which might be generated from historical data, simulations orestimations, etc. Basically the objective is to minimize the sum of thecost, i.e. overall cost, of the edges (i.e. cell-crossing rate,registration traffic or any other traffic sources, etc.) between RA's.The problem of minimizing the radio access traffic (or any other trafficsources) with any capacity type corresponding to any physical or virtualequipments (such as paging traffic capacity) as an upper bound on thesize of the RA is formulated.

Before getting to the details of the proposed invention, some terms usedin the specification may be introduced and defined firstly: A partitionunit (PU) is an element in a wireless communication system, usually acell or a site (comprising 1 to 3 cells in regular circumstances), whichis to be partitioned into RA's. A partition unit pool is a set of PU's.A PLAN is then a record of RA arrangements from a partition on the PUpool.

FIG. 2 clearly exposes a situation of “local minimum” manyRA-partitioning refining procedures are often trapped into. From thefigure, we can easily check and see that, in the case of K-L/F-Malgorithm, every PU belongs to its favorite RA. PU1 favors RA1 becauseof its “personal” consideration; on the other hand, PU2 also favors RA1with the same reason. However, if PU2 joins RA2 instead, then PU1 willbecome to favor RA2 as well due to the action from PU2. It is reasonablethat the current PU1 and PU2 can be grouped together as a new (andbigger) partition unit. This new PU will then favor RA2 now instead ofRA1. Therefore, the new PU (including PU1 and PU2), which is calleddynamic partition unit (DPU), should be moved or swapped to RA2 to bringa better partitioning result.

Most of the conventional RA-partitioning refining methods in this art(including K-L, F-M algorithm, or the modified) are basically a“micro-adjustment” algorithm, which is the reason why the conventionalRA-partitioning refining methods are easily stuck into local minimum.There is indeed much a need in deriving a “macro-adjustment” algorithmwhen we deal with the above-mentioned problem. The idea is then to makethe RA-partitioning refining method an “any-level-adjustment” algorithmby being able to dynamically setting the size and the boundary of thepartition unit. So in the embodiment of the present invention, we callit “iterative RA-partitioning refining method with dynamic partitionunit (DPU)” with the method being K-L or F-M algorithm, etc. Given a PUpool, a PLAN, a set of constraints and a LU cost evaluation function(generalizable to other evaluation functions from different trafficsources), the purpose is to produce a new plan satisfying theconstraints with LU cost (or costs from other traffic sources) as low aspossible.

The detailed procedures of the flow of the proposed invention areorganized in FIG. 3 and each corresponding description will be done asfollows. Before that, again, some further definitions are built up.First, as just put forth, a dynamic partition unit (DPU) is a PU or aset of DPU's. Each DPU can form a tree structure with DPU's as internalnodes and PU's as leaf nodes. Properties of a DPU can be analogized fromthe set of PU's it contains, for example, the paging rate of a DPU isthe sum of that of its containing set of PU's. (So it should be notedthat DPU and PU will be brought up interchangeably throughout.) Second,a dynamic registration area (DRA) comprises a set of DPU's. A DPU pool(DPOOL) is a set of DPU's and a “layer” is a DPU pool. Third, a DPLANwith respect to a layer is a set of DRA's that forms a partition on thelayer (DPU pool).

In the beginning, step 302: Define (i.e. partition) RA's based onpartition units (PU's), is executed. It may either come from theoriginal design of RA partition, or start from the circumstance that acell/site is itself a RA and that further refining is to be done. Afterthat, operation proceeds to step 304, which is the grouping of PU's intoDPU's. In other words, since originally a target problem with PU pooland PLAN input is confronted, they have to be transformed to DPU pooland DPLAN by constructing each DPU to represent each PU.

What follows above is step 306, which is to determine the edgescomprising a plurality of mobility data and represented by a pluralityof mobility rates, which can be determined by a plurality of trafficsources in a service area of a wireless communication system fromhistorical data, simulations or estimations, etc. It is also todetermine the loading condition of the DPU's which fits correspondingloading limit(s) including a plurality of constraints with respect toany physical or virtual equipments in the wireless communication system.

The operation then proceeds to the activation and performance of aRA-partitioning refining method such as K-L, F-M algorithm, or any other“local-minimum tracking procedures” in step 308 to generate better DRApartitioning and better boundaries between the DRA's. What follows isstep 310 posting the question: Does the new RA partition bring lower LUcost after comparing it with the old RA partition? If the new RApartition brings lower LU cost (Yes to step 310), then elements (DPU's)of DRA's will be decomposed in step 312 from DPLAN back to their formergrouping and the process will loop back to the execution of step 306 andkeep running. On the other hand, if the new RA partition doesn't bringlower LU cost after comparing it with the old RA partition, then theproposed algorithm will check if here a DPU itself actually constructs aRA in step 314, or say if a slot, RA, contains only one “top-level” DPU,which means that the DPU is not contained by another DPU. If so, itmeans that no more merging of DPU's is possible and sensible, so theresulting RA partition will just be the final RA-partition arrangement318 and the whole algorithm will come to an end; if not, the DPU's willbe merged into bigger DPU's in step 316 and the process will loop backto step 306 and keep running until the merging procedure can not any bedone (i.e. again, a DPU itself constructs a RA), and so on.

In other words, basically the algorithm is that given a graph partitionrefining problem (GPRP), the K-L, F-M algorithm or any other relatedalgorithm is run on it, say, GPRP_(k) (starting from k=0) and getGPRP_(k)′ (step 308). If any of the methods is effective, then go“upstairs” (step 316) to get a super GPRP, GPRP_(k+1), from GPRP_(k)′,otherwise go “downstairs” (step 312) to GPRP_(k−1)′. Here “upstairs” isdefined as the action constructing a super GPRP from a GPRP and“downstairs” is defined as the action restoring a GPRP from a superGPRP. It should be noted that given a GPRP, there may be many superGPRP's. The upstairs action is then a nondeterministic action, but thedownstairs action, on the other hand, is a deterministic action. So theupstairs action is executed by randomly choosing one super GPRP from allpossible candidates, and the downstairs action is executed by justrestoring the graph to its previous one.

This algorithm is run recursively. If in the process of adjustment,there are good effects generated (i.e. lower LU cost produced), then afiner adjustment is executed, otherwise a rougher adjustment isexecuted. The important thing here to be noticed is on two boundaryconditions. One is that downstairs cannot be executed to GPRP⁻¹, sounder this condition, naturally the same GPRP is used and go to step306. The other is that if a DPU itself constructs a RA already, theoperation ends then.

Here an example is given to illustrate the proposed method (procedure).Given a network topology as follows, with a paging load limit of 18, thegoal is to find a partition on network with as low location updatetraffic as possible between slots of the partition but that total pagingtraffic in each slot of the partition is lower than the load limit 18.In the network topology, each node represents an equipment (physical orvirtual), each label attaching on a node represents the paging trafficload of the equipment, and each number attaching on a link representsthe location update traffic between two equipments. Please refer to FIG.4.

At Step 302, a partition on this network is defined by an arbitrarypartition, a random partition, or an output partition of some partitionrefining procedure first. In this example, a primitive partition whereeach node is taken as a slot of the partition is used. English alphabetsare used here to denote slots of the partition. Please refer to FIG. 5.

At Step 304, each node is considered as a partition unit. A dynamicpartition unit can be seen as a set of partition units or a set ofdynamic partition units. So each partition unit is transferred to adynamic partition unit. At Step 306, since partition units are justtransferred to dynamic partition units, the paging data and locationupdate data have to be rebuilt. Please refer to FIG. 6.

At Step 308, an arbitrary refining procedure can be run. Here aK-L/F-M-based algorithm is used. First, a random node sequence: {1} {5}{6} {2} {4} {7} {10} {3} {8} {9} is assigned. Under this processingorder, nodes are put together if this is good for minimizing inter-slotslocation update traffic. For example, considering node {1}, node {1}will be pushed to slot D, because pushing node {1} to slot D can make alower cost by 50, and is better than pushing node {1} to slot B or E.Considering node {2}, when having two nodes {1} and {4} in slot D, {2}will be pushed to slot D and get a lower cost by 50. Finally thefollowing moves are determined in the same way. Now the LU cost is 190.Please refer to FIG. 7.

At Step 310, since the refining procedure has truly changed thepartition topology and got a lower LU cost from Step 308, Step 312 isexecuted. At Step 312, originally dynamic partition units have to bedecomposed, but there is nothing to decompose because each dynamicpartition unit contains only one partition unit. Then the process loopsback to Step 306. Again, since there is nothing changed, the Step 306 isskipped to go to Step 308.

At Step 308, another random sequence is generated: {5} {7} {6} {10} {8}{1} {4} {3} {2} {9}. Using this sequence, we run the K-L/F-M-basedprocedure. In this turn, there is nothing changed, which means that allnodes are stable. The solution is obviously trapped into a localminimum. Now the LU cost is 190. At Step 310, since a lower LU costcannot be gotten through Step 308, Step 314 is executed. At Step 314,since not every slot contains only one top-level DPU, Step 316 isexecuted.

At Step 316, dynamic partition units are to be merged into bigger ones.Since each bigger DPU must be included in some partition slot, onlyDPU's in the same slot can be merged. Still another random sequence: {1}{2} {3} {8} {9} {7} {10} {4} {5} {6} is gotten. Under this sequence,when node {1} is considered, node {1} and node {4} are merged justbecause between {2} and {4} (in the same slot with node {1}), node {4}has the biggest LU cost with node {1}. When node {2} is considered,since node {1} and node {4} are processed already, node {2} can not bemerged with anyone. Please refer to FIG. 8.

With the process looping back at Step 306, the paging traffic and LUtraffic for each bigger dynamic partition units have to be recalculated.Please refer to FIG. 9.

At Step 308, another random sequence is gotten: {{1}, {4}} {{5}} {{6},{7}} {{2}} {{3}, {8}} {{9}, {10}}. Under this sequence, considering node{{1}, {4}}, pushing it to slot F gets a lower LU cost. Consider node{{2}}, when slot F contains nodes {{1}, {4}}, {{6}, {7}}, {{5}}, pushingnode {{2}} to slot F can get a lower LU cost, but this action will pullup the paging load of F to 20 which exceeds the load limit constraint18. So node {{2}} is pushed to slot H instead. Please refer to FIG. 10to see the result of Step 308.

At Step 310, since lower LU cost is gotten at Step 308, Step 312 isexecuted to return to the previous network topology, and get FIG. 11.

With the process looping back at Step 306, the original paging load andLU traffic data will be recovered. At Step 308, K-L/F-M is run, butnothing is changed because the total paging loads of slot F and H areclose to paging load limit 18. At Step 310, since lower LU cost cannotbe gotten, Step 314 is executed. At Step 314, not every slot containsonly one top-level DPU, so go to Step 316. At Step 316, another randomsequence is gotten: {7} {9} {3} {8} {2} {6} {5} {1} {10} {4}. Under thissequence, the merging procedure is run again. Then at Step 306, pagingloads and LU traffic are calculated. Please refer to FIG. 12.

At Step 308, K-L/F-M is run, but nothing is changed. At Step 310, sincethere is nothing changed at Step 308, Step 314 is executed. At Step 314,not every slot contains only one top-level DPU, so go to Step 316. AtStep 316, another random sequence is gotten: {{2}} {{3}, {8}} {{1}, {5}}{{6}, {7}} {{9}, {10}} {{4}}. Under this sequence, the merging procedureis run again. With the process looping back at Step 306, the pagingloads and LU traffic are calculated again. Please refer to FIG. 13.

At Step 308, K-L/F-M is run, but nothing is changed. At Step 310, sincethere is nothing changed at Step 308, Step 314 is executed. At Step 314,not every slot contains only one top-level DPU, so go to Step 316. AtStep 316, another random sequence is gotten: {{{9}, {10}}} {{{4}}, {{1},{5}}} {{{2}}, {{3}, {8}}} {{{6}, {7}}}. Under this sequence, the mergingprocedure is run. At Step 306 again, the paging loads and LU traffic arecalculated. Please refer to FIG. 14.

At Step 308, K-L/F-M is run, but nothing is changed. At Step 310, sincethere is nothing changed at Step 308, Step 314 is executed. At Step 314,since both F and H contain only one top-level DPU, so Step 318 isexecuted. Slot F and H are to be the final partition P={F, H}={{4, 1, 5,6, 7}, {2, 3, 8, 9, 10}}.

It should be noticed that the method disclosed in the embodiment of thepresent invention is for use in all different kinds of wirelesscommunication systems, including not only the second generation wirelessnetworks such as GSM, CDMA and PDC, but also more advanced systems suchas 2.5 G systems like GPRS and EDGE, 3G systems like UMTS/WCDMA,CDMA2000 and TD-SCDMA, and other wireless communication systems such asPHS and Wireless LAN/IPv6 networks. The terms used in different systemsmay be different but the concept is similar. When it comes to theaddressed representative registration area (RA) partitioning refiningmethod with DPU, the concept of the registration area (RA) just coversthe location area (LA) of GSM system, the routing area (also RA) ofpacket-switched or 3 G systems, registration location area(RLA)/overlapping location area (OLA) and paging area of PDC and PHS,cell area (CA) of 3 G systems, as well as UTRAN Registration Area ofUMTS/WCDMA.

While the invention has been described by way of an example and in termsof a preferred embodiment, it is to be understood that the invention isnot limited thereto. On the contrary, it is intended to cover variousmodifications, similar arrangements and procedures, and the scope of theappended claims therefore should be accorded the broadest interpretationso as to encompass all such modifications, similar arrangements andprocedures.

1. A method for determining a plurality of registration areas in awireless communication system, wherein the wireless communication systemcomprises a plurality of first registration areas, and each of the firstregistration areas comprises at least one of a plurality of firstpartition units, the method comprising the steps of: performing aregistration area determining procedure according to a plurality ofmobility data corresponding to the first partition units to determine aplurality of second registration areas, wherein each of the secondregistration areas comprises at least one of the first partition units;comparing an overall cost of the first registration areas with anoverall cost of the second registration areas; determining a pluralityof second partition units, including a dynamic partition unit, and aplurality of mobility data corresponding to the second partition unitsand the dynamic partition unit according to the result of comparison,wherein at least the dynamic partition unit is generated by combining atleast two of the first partition units when the overall cost of thefirst registration areas is lower than or equal to the overall cost ofthe second registration areas, and at least the dynamic partition unitis generated by partitioning one of the first partition units when theoverall cost of the first registration areas is higher than the overallcost of the second registration areas; and performing the registrationarea determining procedure according to the mobility data correspondingto the second partition units and the dynamic partition unit todetermine a plurality of third registration areas, wherein each of thethird registration areas comprises at least one of the second partitionunits, and one of the third registration areas includes the dynamicpartition unit.
 2. The method of claim 1, wherein the method is executedrecursively until a plurality of (n+1)^(th) registration areas andn^(th) partition units are determined that each of the (n+1)^(th)registration areas includes only one n^(th) partition unit and theoverall cost of the (n)^(th) registration areas is smaller than or equalto the overall cost of the (n+1)^(th) registration areas.
 3. The methodof claim 1, wherein the mobility data at least include a plurality ofmobility rates.
 4. The method of claim 3, wherein the mobility rates aredetermined by a plurality of traffic sources in the wirelesscommunication system through at least one of the following operationswhich are gathering historical data, simulation and estimation.
 5. Themethod of claim 1, wherein the second partition units are determinedbased on a plurality of loading limits of the wireless communicationsystem.
 6. The method of claim 5, wherein the loading limits at leastinclude a plurality of constraints corresponding to any physical orvirtual equipments in the wireless communication system.
 7. The methodof claim 1, wherein the registration area determining procedure is atleast one of the K-L algorithm and the F-M algorithm.
 8. The method ofclaim 1, wherein the registration area is determined by at least one ofthe following: a location area (LA) of a GSM system, a routing area (RA)of a packet-switched or a 3 G systems, a registration location area(RLA)/overlapping location area (OLA) and a paging area of a PDC and aPHS system, a cell area (CA) of a 3 G systems, and an UTRAN RegistrationArea of a UMTS/WCDMA system.
 9. The method of claim 1, wherein when thefirst partition units are non-partitionable, generating the secondpartition units by combining at least two of the first partition unitsis performed.